Cigarette smoking rates In American Indian (Al) tribes are anrtong the highest in the U.S., and smoking prevalence is increasing among Al youth. More than a trillion mobile-phone text messages are sent every year, and young adults spend an average of 13 hours per week texting. Smoking cessation interventions aimed at young adults are therefore ideally suited for delivery by mobile phones. In this project we will implennent a text niessaging-based smoking cessation intervention at 6 tribal colleges and universities (TCUs) in Montana, reaching a concentrated group of 1500 Als who are young, educated, and technologically literate. Our approach is based on the successful STOMP (STOp smoking by Mobile Phone) program, adapted to incorporate approaches that embrace the critical role of tribal members in addressing the smoking epidemics in their communities. The technical aims of this study will determine (1) the acceptability and relevance of the STOMP text messaging-based smoking cessation program, (2) the cultural appropriateness of STOMP for use in this population, (3) baseline smoking data such as smoking status, age of initiation, nicotine dependence, quit attempt history, and (4) verification of smoking cessation using cotinine assays. The scientific aims of this study will determine (1) the effectiveness of the adapted STOMP (A-STOMP) text messages vs. standard informational text messages in smoking cessation among TCU students and estimate the accuracy of self-reported cessation by salivary cotinine verification, (2) quantify the effect of A-STOMP text messages vs. standard informational text messages on intermediate smoking variables in participants who continue to smoke, and (3) evaluate TCU-specific contextual factors as potential cross-level effect modifiers of the intervention for individual smoking cessation outcomes. Smoking is a leading cause of preventable death and is Increasing among young Als, creating a critical need for novel strategies to support smoking cessation attempts that can reach dispersed, rural populations. Our methods will strengthen our tribal partners' expertise in and support for intervention research.